Turbine housings of sheet metal have been suggested in various documents. Examples are U.S. Pat. No. 2,801,043; DE-A-100 22 052 or WO 01/94754. The advantage of such a construction resides in a simple production possibility and little weight as compared with cast turbine housings. Furthermore, the so-called LSI technique should be mentioned, i.e. housings having an insulated air gap.
Apart form the production problems, a different problem in turbochargers, which forms the basis of the present invention, is the fact that a catalyst, after starting the combustion motor, needs some time to attain its operating temperature in which it develops its full efficiency. If the turbocharger is operating during this time, it takes over part of the heat of the exhaust gas so that the gas reaching the catalyst has already cooled down a bit so that the catalyst needs more time to reach its normal operational temperature. This time is still prolonged when using cast housings for the turbocharger, because they have a higher heat absorption capacity.